Parameters for objective-c class?

It sounds like you need to read the primer:
http://developer.apple.com/library/...mer/index.html#//apple_ref/doc/uid/TP40007594

(What book are you reading)

 

Very briefly:
You are used to a constructor that, when called, will allocate space for a new object implicitly, then begin a method that can accept arguments to initialize the object's state. The new keyword is used in combination with the class name and any arguments to a constructor.

In Objective-C, things are similar, but are broken into an alloc and an init stage. Passing the alloc message to a class object will return a pointer to space for the new object, which will be uninitialized. The first message that is passed to this new object is an init message. Traditionally initializers start with init, then describe any parameters i.e. initWithString:. The initializer can accept arguments which can be used to setup your object's state. You also call the parent class's initializer in this method. Sometimes an initializer will return a pointer to a different object (a singleton for a specific init value, say) than was returned from alloc, so the normal pattern is:

Code:

myAwesomeObject *awesomeSix = [[myAwesomeObject alloc] initWithInt: 6];

This really isn't that different, but the alloc and init are more explicit than new and a constructor.

This doesn't cover factory methods, obviously, but that's for another day.

For your example, you'd have an init method called initWithName:andAge:. In this method you'd call init on the superclass, then set your ivars using the passed in values. Assuming properties with synthesized getters/setters:

Code:

- (id) initWithName: (NSString *) newName andAge: (int) newAge {
  if(self = [super init]) {
    [self setName:newName];
    [self setAge:newAge];
  }
  return self;
}

You'd call this:

Code:

mmPerson *myBuddyMax = [[mmPerson alloc initWithName:@"Max Sblongrass" andAge:22]];

-Lee

Edit: ended up not-so-brief. You asked about requiring parameters, not just allowing them. This is a bit tough because NSObject responds to init with no parameters. You could override init and throw an exception if it's used, but I'd say the best way to go is to only document the init method with the parameters.

 

Firstly

Code:

mmPerson *myBuddyMax = [[mmPerson alloc] initWithName:@"Max Sblongrass" andAge:22];

Secondly Objective-C uses a two stage initializer, the reason for this is to separate allocation from initialization with +allocWithZone: and what people call "the designated initializer"

Most people will not override -init to throw an exception, they would override it to call their own designated initializer with default values (but I guess if you REALLY want to require them...)

In the above example:

Code:

- (id)init {
return [self initWithName: @"unnamed" andAge: 0];
}

 

Absolutely right. I was trying to devise a way to *require* the use of a paramterized init method, like you could do by only having one constructor with parameters in Java and couldn't come up with one.